Using data collected from the 1996 to 2013 proxy seasons, Fenwick & West tracked the number of women serving on boards and executive management teams of companies in the Silicon Valley 150 index. The results were astonishing.

In the 2013 proxy season,more than 80% of Silicon Valley 150 companies had only one woman director or none at all.

And we're not just talking about four-person startups; the average number of employees in these 150 companies is 8,500.

The report optimistically notes that there was a general upward trend over the survey period: between 1996 and 2013, the rate of women board directors grew 320% in the SV 150 and 80% in the S&P 100.

But as Vivek Wadhwa, a fellow at Stanford University's Rock Center for Corporate Governance who is writing a book on women in tech, pointed out in an email to Business Insider, Silicon Valley's higher growth rates signify just how much room they have to grow to reach gender equity on boards.

The report notes that one factor in these skewed distributions is the board's size. S&P 100 companies tend to have more women directors than SV 150 companies in absolute terms: The S&P 100 average is 2.4 women, compared to the SV 150 average of 0.8.

But the difference is slightly less pronounced when measured as a percentage of the total number of directors: The S&P 100 average is 19.9% of directors, and the SV 150 average is 9.1%.

Fenwick & West
Yet if the recent brouhaha over Twitter's decision to go public with an entirely male board is any indication, it's clear that there is more keeping women from executive boardrooms than simply the size of the company. (Twitter appointed Marjorie Scardino to its board soon after it went public. Although as Vauhini Vara notes, having one woman on a board of eight is hardly something to write home about.)

Before Twitter hired Scardino to its board, Glimpse Labs CEO Elissa Shevinsky argued that companies like Twitter are stymied by a lack of qualified female candidates and would hire more women executives if they could find them. She also said that women board members are only valuable if they "have expertise in running a large public company."

However, this idea has been refuted by a study by the Credit Suisse Research Institute, which looked at 2,360 public companies and found that over six years the share price of large-capitalization companies with at least one woman on the board outperformed companies with no women on their boards by 26%. More compellingly, they found that it was the presence of the women at the table — "not necessarily the performance of the minority individuals" themselves — that enhanced the result. "The majority group improves its own performance in response to minority involvement," the report reads.

While Fenwick & West's findings are frankly abysmal, Wadhwa believes that the climate in Silicon Valley is getting better for women, albeit slowly. He cites three reasons for his optimism:

"The cost of developing technology is dropping dramatically, so venture capital has become irrelevant."

"Women are becoming more confident and assertive — particularly the next generation."

"Women are networking and helping each other, [and] men are mentoring women."

Given the cultural, reputational, and financial benefits of having a more diverse board, in addition to increased efforts to get women into computer science and engineering courses early, Wadhwa believes the upward trend found in Fenwick & West's study will continue in Silicon Valley.

But as Maria Klawe, president of Harvey Mudd College and a board member at Microsoft, told Reuters: "The companies that want to do it will do it. Those who don't will not. This stuff doesn't happen by chance."